Contact Form 7 – how manipulate data before mail is sent? [closed]

This could be outdated but I suggest turning on your debug_log and print the following code in the before_send_mail hook:

error_log( print_r( $submission, 1 ) );

That will give you an idea of what you’re dealing with. The below may be outdated but I think what you need to modify is the $submission->mail array.